Pseudo-affective visceromotor responses and HPA axis activation following colorectal distension in rats with increased cholinergic sensitivity

Abstract We analysed visceromotor (VMR) and corti-costerone responses to colorectal stimuli under controlconditions and following acoustic stress in rats selec-tively bred for increased sensitivity to cholinergic ag-onists, the Flinders Sensitive Line (FSL) rats, comparedwith Flinders Resistant Line (FRL) rats. FSL rats dem-onstrated a significant VMR response at the smallestdistensionpressure,whereasnoresponsewasevidentinFRL controls. FSL rats also demonstrated enhancedVMR responses at both larger distension levels com-pared with FRL rats. Colorectal distension (CRD) pro-duced significant increases in serum corticosteronelevels, which were comparable in FRL and FSL. Noisestress induced divergent corticosterone responses inFRL and FSL, but did not affect VMR to CRD in eithergroup. These data suggest that FSL rats show alteredVMR responses to CRD and disturbed hypothalamic–pituitary–adrenal axis responses to acute stress.Keywords cholinergic sensitivity, corticosterone,psychological stress, visceral hyperalgesia, viscero-motor responses.